Neuroimaging techniques are used to investigate the function of the human brain, but it is believed that none are currently able to accurately localize neuronal activity with a suitably high spatial and temporal resolution. See, e.g., Kwong, et al., Dynamic magnetic resonance imaging of human brain activity during primary sensory stimulation. Proc. Natl. Acad. Sci. USA. 89, 5675-5679 (1992); Bandettini et al., Time course EPI of human brain function during task activation, Magn. Reson. Med. 25, 390-397 (1992); Ogawa, S. et al. Intrinsic signal changes accompanying sensory stimulation: functional brain mapping with magnetic resonance imaging. Proc. Natl. Acad. Sci. USA. 89, 5951-5955 (1992); Hillyard et al., Electrical signs of selective attention in the human brain. Science. 182, 177-180 (1973); and Hämäläinen et al., Magnetoencephalography—theory, instrumentation, and applications to noninvasive studies of the working human brain. Rev. Mod. Phys. 65, 413-497 (1993).
Noninvasive neuroimaging techniques are arguably the most widely used tools to study the structure and function of the human brain in vivo. Functional magnetic resonance imaging (fMRI) based on the blood oxygenation level-dependent (BOLD) contrast benefits from a relatively high spatial resolution and a whole-brain coverage, but it relies on hemodynamic modulations and is thus only an indirect measure of neuronal activity, and with a very low temporal resolution. Conversely, scalp-recorded electroencephalography (EEG) and magnetoencephalography (MEG), which are more direct measures of neural activity, benefit from a high temporal resolution and can capture neuronal oscillations. However, they are limited by a poor spatial resolution, primarily due to the inverse problem for localizing sources of electrical activity measured on the surface of a volume. Multi-modal imaging such as simultaneous EEG/fMRI can provide complementary information about brain activity, but cannot truly achieve a high spatial and temporal accuracy simultaneously due to the disparate signal sources.